U.S. patent number 10,184,388 [Application Number 14/954,046] was granted by the patent office on 2019-01-22 for engine piston.
This patent grant is currently assigned to Caterpillar Inc.. The grantee listed for this patent is Caterpillar Inc.. Invention is credited to Chad Ahmad.
United States Patent |
10,184,388 |
Ahmad |
January 22, 2019 |
Engine piston
Abstract
A piston for an internal combustion engine includes a piston
body forming a crown portion and a skirt portion, the crown portion
forming a generally concave bowl extending symmetrically around the
piston body with respect to an axis of symmetry of the crown
portion. The bowl forms a first lip and a second lip that are
arranged in a stepped configuration along a side margin of the
bowl. A depressed ledge having a generally annular shape is further
formed in the crown portion, the depressed ledge including a flat,
annular surface extending along a plane that is parallel to a plane
defined by the generally flat crown surface.
Inventors: |
Ahmad; Chad (Peoria, IL) |
Applicant: |
Name |
City |
State |
Country |
Type |
Caterpillar Inc. |
Peoria |
IL |
US |
|
|
Assignee: |
Caterpillar Inc. (Deerfield,
IL)
|
Family
ID: |
58692890 |
Appl.
No.: |
14/954,046 |
Filed: |
November 30, 2015 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F02B
23/0696 (20130101); F02B 23/0693 (20130101); F02B
23/0672 (20130101); F02F 3/26 (20130101); Y02T
10/12 (20130101); F16J 1/00 (20130101); Y02T
10/125 (20130101) |
Current International
Class: |
F02F
3/00 (20060101); F16J 1/00 (20060101); F02B
23/06 (20060101); F02F 3/26 (20060101) |
Field of
Search: |
;123/197.2,193.1,193.6
;92/172,181R,208 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
101769195 |
|
Jul 2010 |
|
CN |
|
0845589 |
|
Jun 1998 |
|
EP |
|
2752563 |
|
Jul 2004 |
|
EP |
|
2752564 |
|
Jul 2004 |
|
EP |
|
1630380 |
|
May 2011 |
|
EP |
|
WO 2008/078270 |
|
Aug 2005 |
|
WO |
|
Primary Examiner: Moubry; Grant
Attorney, Agent or Firm: Leydig, Voit & Mayer, Ltd.
Claims
I claim:
1. A piston for an internal combustion engine, comprising: a piston
body forming a crown portion and a skirt portion, the skirt portion
including a pin bore that is arranged to receive a pin for
connecting the piston to a connecting rod, the skirt portion
further forming two guide surfaces along outer margins of the skirt
portion, the crown portion forming a generally cylindrical surface
surrounding the crown portion, and a generally flat crown surface
extending around an end of the crown portion disposed opposite the
skirt portion; wherein the generally flat crown surface forms a
generally concave bowl within the generally cylindrical surface,
the generally concave bowl extending symmetrically around the
piston body with respect to an axis of symmetry of the crown
portion; wherein the generally concave bowl forms a first lip and a
second lip that are arranged in a stepped configuration along a
side margin of the generally concave bowl; and wherein the crown
portion further forms a depressed ledge having a generally annular
shape, the depressed ledge including a flat, annular surface
extending along a plane that is parallel to a plane defined by the
generally flat crown surface, the depressed ledge disposed between
the generally flat crown surface and the generally concave bowl;
wherein the piston body further forms a first chamfer surface
between the depressed ledge and the generally flat crown surface,
the first chamfer surface disposed along a radially outward edge of
the depressed ledge and having a first radius of curvature; wherein
the depressed ledge includes an inner edge that extends annularly
around an entire radially inward periphery of the depressed ledge;
wherein the piston body further forms a first surface at an
uppermost region of the side margin of the generally concave bowl
along a radially inward portion of the depressed ledge, the first
surface forming the first lip having a generally convex shape;
wherein the first lip extends peripherally around the generally
concave bowl and extends radially inward with respect to an inner
edge and the first surface; wherein the piston body further forms a
second surface, the second surface having a generally concave shape
that is formed at a second radius of curvature, the second surface
forming the second lip having a generally convex shape, the second
surface separated by the first surface along the first lip; wherein
the piston body further forms a third surface, the second lip
separating the second surface from the third surface, the third
surface having a generally concave shape that is formed at a third
radius of curvature; wherein the third surface extends between the
second lip and a central portion of the generally concave bowl, the
central portion of the generally concave bowl having a generally
conical, convex shape; wherein an inner diameter (d) of the piston,
the inner diameter being defined by a radially outermost point of
the second surface with respect to the axis of symmetry, is
selected to be equal or larger than a diameter of a stable fuel
plume for a particular crankshaft angle range in which fuel is
provided into a cylinder of an engine that the piston is operating;
and wherein the second radius of curvature is equal to the third
radius of curvature.
2. The piston of claim 1, wherein an outer diameter (D), which
extends around an outer edge of the first chamfer surface, is
selected such that a ratio D/d is equal to 0.24.
3. The piston of claim 1, wherein an angle (7), which is measured
from a pin centerpoint to the first lip is about 65 degrees.
4. The piston of claim 1, wherein a height (H2) of a centerpoint
for the third surface is 66% of a height (H1) of a centerpoint for
the second surface with respect to a lowermost point in the
generally concave bowl.
5. The piston of claim 1, wherein the second radius of curvature
(R2) and the third radius of curvature (R3) are selected such that
R2=R3=0.197*d.
6. The piston of claim 1, wherein a depth (h) of the depressed
ledge with respect to the generally flat crown surface is selected
to be about 6% of the inner diameter (d).
7. The piston of claim 1, wherein a fourth radius of curvature (R4)
of the first surface is selected to be equal to the second radius
of curvature (R2).
8. The piston of claim 7, wherein R2=R3=R4.
9. The piston of claim 8, wherein d=117.5/2*R.
Description
TECHNICAL FIELD
This disclosure relates generally to internal combustion engines
and, more particularly, to pistons operating within engine
bores.
BACKGROUND
Internal combustion engines typically include one or more pistons
interconnected by connecting rods to a crankshaft. The pistons are
typically disposed to reciprocate within bores formed in a
crankcase. A typical piston includes a head portion, which at least
partially defines a combustion chamber within each bore, and a
skirt, which typically includes a pin opening and other support
structures for connection to the connecting rod of the engine. In
general, a piston is formed to have a generally cupped shape, with
the piston head forming the base, and the skirt portion being
connected to the base and surrounding an enclosed gallery of the
piston. In typical applications, lubrication oil from the engine is
provided within the gallery of the piston during operation to
convectively cool and lubricate various portions of the piston.
A typical piston head also includes an outer cylindrical wall
having one or more circumferentially continuous grooves formed
therein. These grooves typically extend parallel to one another and
are appropriately sized to accommodate sealing rings therewithin.
These sealing rings create sliding seals between each piston and
the crankcase bore it is operating within. Typically, the groove
located closest to the skirt of the piston accommodates a scrapper
ring, which is arranged to scrape oil clinging on the walls of the
piston bore during a down-stroke of the piston. Oil that may remain
wetting the walls of the bore following the down-stroke of the
piston may enter the combustion chamber and combust during
operation of the engine.
In general, the piston operates by reciprocating within a bore
formed in a cylinder case of the engine, which creates a variable
volume that can compress a fuel/air mixture provided therein. The
combusting fuel/air mixture expands and pushes the piston to
increase the variable volume, thus producing power. Fuel can be
provided directly or indirectly within the variable volume, while
air and exhaust gas is provided or removed from the variable volume
through one or more intake and exhaust valves that selectively
fluidly connect the variable volume with intake and exhaust
collectors.
The materials used to construct the walls of the engine cylinders,
the piston, the various valves associated with the variable volume,
and other surrounding engine structures, are selected to withstand
high temperatures and pressures that are present during engine
operation. Various features of the piston are also shaped to
promote the efficient burning of fuel within the piston,
reliability of the various engine components associated with the
engine cylinders, and other considerations. However, it is always
desired to increase the reliability and service life of these and
other engine components, as well as promote the efficient operation
of the engine in terms of reducing fuel consumption and emissions
and increasing power and efficiency.
One example of an engine piston having shaped features to promote
efficient fuel burning can be seen in U.S. Pat. No. 7,942,126 (the
'126 patent), which is directed to a "Method for Operating an
Internal Combustion Engine and Internal Combustion Engine for such
a Method." The '126 patent describes a piston top having integrally
formed therein a piston recess which merges into an essentially
annular stepped space, and an injector forming injection jets
directed toward the stepped space.
According to the '126 patent, the injection jets are deflected by
the stepped space into a first part quantity of fuel, which is
directed in an axial direction and a radial direction into the
piston recess, and a second part quantity of fuel is deflected in
the axial direction and the radial direction over the piston top
and third part quantities of fuel are deflected into a
circumferential direction so as to impinge one onto the other in
the circumferential direction and to be deflected radially
inwardly. As can be appreciated, for the engine of the '126 to
operate as described, the start of injection and the injection
duration must be precisely coordinated with one another and with
the crank angle of the internal combustion engine. Such
coordination, however, makes it difficult to operate the engine
efficiently over a broad range of engine operating conditions and
environmental factors such as temperature, which may affect engine
operation.
BRIEF SUMMARY OF THE DISCLOSURE
In one aspect, the disclosure describes a piston for an internal
combustion engine. The piston includes a piston body forming a
crown portion and a skirt portion. The skirt portion includes a pin
bore that is arranged to receive a pin for connecting the piston to
a connecting rod. The skirt portion further forms two guide
surfaces along outer margins of the skirt portion. The crown
portion forms a generally cylindrical surface surrounding the crown
portion, and a generally flat crown surface extending around an end
of the crown portion disposed opposite the skirt portion. A
generally concave bowl is formed in the crown surface and within
the generally cylindrical surface, the generally concave bowl
extending symmetrically around the piston body with respect to an
axis of symmetry of the crown portion. The generally concave bowl
forms a first lip and a second lip that are arranged in a stepped
configuration along a side margin of the generally concave bowl.
The crown portion further forms a depressed ledge having a
generally annular shape. The depressed ledge includes a flat,
annular surface extending along a plane that is parallel to a plane
defined by the generally flat crown surface, and is disposed
between the generally flat crown surface and the generally concave
bowl.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a fragmented view of a piston in accordance with the
disclosure.
FIG. 2 is an enlarged detail of a cross section of the piston shown
in FIG. 1.
FIG. 3 is a partial cross section of the piston shown in FIG.
1.
DETAILED DESCRIPTION
This disclosure relates to pistons for use in internal combustion
engines. In one aspect, the disclosure describes an embodiment for
an engine piston having features that can set up flow fields and
turbulence to promote combustion of fuel within the cylinder over a
wider range of crankshaft angles than was attainable with previous
piston designs. Such features of the piston, depending on the type
of engine operation, for example, spark ignition or compression
ignition, can operate to contain, mix and/or direct various fuel
containing masses within the piston to increase engine efficiency,
decrease heat rejection, shorten burn time, and also control
component temperatures, thus increasing component reliability and
service life. As discussed herein, the mixing or directing of
material within the cylinder may occur at least for an instant and
may last no more than a few thousandths of a second while an
injection of fuel and/or a combustion flame is present within the
cylinder, or over portions of that period.
For purpose of illustration of certain features of an engine piston
in accordance with the disclosure, a partially fragmented view of a
piston 100 for an engine is shown from a side perspective in FIG.
1. The piston 100 includes a crown portion 102 and a skirt portion
104. The skirt portion 104 forms a pin bore 106 that accommodates a
pin (not shown) used to pivotally connect the piston to a
connecting rod (not shown), which is connected to an engine
crankshaft (not shown) in the known fashion. The skirt portion 104
further includes two guide surfaces 105 disposed on diametrically
opposite sides of the piston 100. In an alternative embodiment, the
guide surfaces may be integrated into a single guide surface
extending substantially around the piston. In the illustrated
embodiment, the two guide surfaces 105 extend at least along cross
sections of the piston that include a piston cross section 103,
which is shown in FIG. 1 and which is perpendicular to a
centerline, C/L, of the pin bore 106. On either side of the piston
100, the two guide surfaces 105 may extend over two angular
portions of the periphery of the piston.
The crown portion 102 forms a series of channels extending in
parallel to one another that can accommodate piston rings, oil
scrapper rings and other components. In the illustrated embodiment,
two piston ring grooves 110 and one oil collection groove 111 are
formed in the outer cylindrical wall 109. The piston ring grooves
110 accommodate ring seals (not shown) that slidably and generally
sealably engage the walls of the engine cylinder in which the
piston 100 is reciprocally disposed, and the oil collection groove
111 collects oil, which is then allowed to flow back down into the
engine. An outer diameter of the two guide surfaces 105 is arranged
such that the piston is prevented from rotating or binding within
the bore in which it is reciprocally disposed during operation.
Regarding other functional features of the piston 100, in reference
to the orientation of the piston 100 shown in FIG. 1, the crown
portion 102 forms a bowl 114 having generally a concave shape. The
bowl 114 is surrounded by a rim 116. The rim 116 is centrally
disposed relative to an annularly shaped, flat, crown surface 118.
The crown surface 118 is disposed around the rim 116 of the bowl
114. A detailed, section view of the bowl 114 is shown in FIG. 3,
and an enlarged detail view of a side portion of the bowl is shown
in FIG. 2. As can be seen from these figures, the bowl 114 forms a
frusto-conical central portion 117 around a depression 108 that is
centrally located in the bowl 114, which can accommodate an
injector tip (not shown) when the piston 100 is installed in an
engine and assumes a top-dead-center position in the cylinder. The
rim 116, central portion 117, and depression 108 are all
concentrically disposed in the embodiment shown with respect to an
axis of symmetry 112 (shown in FIG. 3) of the bowl 114. The
frusto-conical central portion 117 may be formed at an included
angle, .beta., of about 120 degrees around, and with respect with,
the axis of symmetry 112. Accordingly, as shown, a floor angle, a
(denoted in FIG. 3), which is the acute angle between the slope of
the conical central portion 117 and the crown surface 118, is 30
degrees.
The bowl 114 advantageously forms various features along its side
margin or outer portion 115, which operate to improve engine
operation and permit injection of fuel over a wide range of engine
crankshaft angles. In the embodiment shown in FIGS. 1-3, the bowl
114 forms a depressed ledge 200 that extends annularly around the
bowl 114 immediately radially inwardly with respect to the rim 116.
More specifically, the depressed ledge 200 is an annularly shaped,
flat surface that extends along a plane that is parallel to a plane
defined by the crown surface 118. An outer or first chamfer surface
202 is formed between the rim 116 and the depressed ledge 200 along
a radially outward edge of the depressed ledge 200 with respect to
the axis of symmetry 112. The first chamfer surface 202 is formed
at a first radius, R1 (denoted in FIG. 3).
The depressed ledge 200 includes an inner edge 204 that extends
annularly around an entire radially inward periphery of the
depressed ledge 200. In the embodiment shown, the inner edge 204 is
formed as a chamfered surface having a radius of about 1 mm or
greater. The inner edge 204 of the depressed ledge 200 provides a
transition between the depressed ledge 200 and a first surface 206.
In the orientation of the piston 100 shown in the figures, the
first surface 206 is formed at an uppermost region of the outer
margin of the bowl 114, i.e., a region that is closest to the crown
surface 118 along the axis of symmetry 112. As shown, the first
surface 206 has a generally convex shape formed at a radius, R4,
but may alternatively have a concave or conical cross section
profile.
At a radially inward portion, the first surface 206 forms a first
lip 208 having a generally convex shape. The first lip 208 extends
peripherally around the bowl 114 and extends radially inward with
respect to the inner edge 204 and the first surface 206. The first
lip 208 separates the first surface 206 from a second surface 210.
The second surface 210 has a generally concave shape that is formed
at a second radius, R2 (denoted in FIG. 3). In a radially inward
(or, downward with respect to the bowl) edge, the second surface
210 forms a second lip 212. The second lip 212 separates the second
surface 210 from a third surface 214. The third surface 214 has a
generally concave shape that is formed at a third radius, R3
(denoted in FIG. 3). The third surface 214 extends between the
second lip 212 and the central portion 117, which meets the third
surface 214 in a smooth fashion, as shown, tangentially.
As can be appreciated, the dimensions of the various features of
the piston 100 may depend on various parameters, including an
overall diameter of the piston 100, a desired compression ratio of
the engine in which the piston 100 will be used, and others.
However, the various features may be formed at particular
geometrical ratios, or ranges of ratios, to achieve desired
results.
To further illustrate the operation of the various features of the
piston 100, it should be appreciated that the piston will operate
in an engine having a fuel injector disposed and configured to
inject fuel directly into the combustion cylinder of the engine, in
which the piston reciprocally operates. As is known, the axial
position of the piston within an engine cylinder is correlated with
a rotation angle of the engine crankshaft. As such, particular
ranges of the axial position of the piston within the cylinder may
also be correlated with particular ranges of crankshaft rotation
with respect to the particular respective cylinder. It should also
be appreciated that the injectors used to provide the fuel into the
cylinder during engine operation are configured to spray one or
more streams of fuel into the cylinder at particular locations and
times during operation. Fuel injectors are known to have nozzle
openings that provide fuel jets at particular angles with respect
to a cylinder bore centerline. Those jets, which typically open in
a conical fashion as they travel away from the injector tip, define
a generally cylindrical fuel plume that can have a plume diameter
at various axial locations along the cylinder bore centerline. The
plume, which may begin as a collection of individual streams, may
take some time, for example, 0.7 ms, to fully develop or become
stable after initiation of an injection event.
Accordingly, the various features of the piston include an inner
diameter, d (denoted in FIG. 3), which is generally defined by the
radially outermost point of the second surface 210, and is adjacent
to the inner edge 204 of the depressed ledge 200. The inner
diameter, d, surrounds the generally concave portion of the bowl
114 and can be selected such that it is consistent with, i.e. equal
or large to, the diameter of a stable fuel plume for a particular
crankshaft angle range in which fuel is provided into the cylinder
that the piston 100 is operating. The outer diameter, D, which
extends around the outer edge of the first chamfer surface 202, may
be selected based on a desired ratio with respect to the inner
diameter, d. In the illustrated embodiment, the ratio D/d is equal
to 0.24 for nominal dimensions of the piston 100. Other dimensions
include an angle, .gamma. (denoted in FIG. 1), which is measured
from the pin centerpoint to the first lip 208, that is about 65
degrees.
In the illustrated embodiment, the second radius, R2, of the second
surface 210, and the third radius, R3, of the third surface 214,
are equal. When the heights of their respective center-points for
forming the curved surfaces are considered, a height H2 (denoted in
FIG. 3) of the centerpoint for the third surface 214 is 66% of the
height H1 (denoted in FIG. 3) of the centerpoint for the second
surface 210, with respect to a lowermost point in the bowl 114.
Regarding the radii R2 and R3, each is selected such that
R2=R3=0.197*d, where d denotes the inner diameter, d, described
above. The depth, h (denoted in FIG. 3) of the depressed ledge 200
with respect to the crown surface 118 is selected to be about 6% of
the inner diameter, d. A radius, R4, of a convex-shaped first
surface 206 is selected to be equal to the radii R2 and R3.
Finally, the diameters R2, R3 and R4, are selected based on the
inner diameter, d, according to the following relation:
d=117.5/2*R, where R=R2, R3 or R4.
INDUSTRIAL APPLICABILITY
The present disclosure is applicable to pistons for internal
combustion engines, which can be used in any application such as
land or marine based applications, as well as for mobile or
stationary applications. The various embodiments for piston
features described herein have been found to have advantages in
improving engine operation by increasing power output, decreasing
fuel consumption and also decreasing emissions.
In general, the piston 100 forms various features that operate to
redirect and/or contain various moving masses within the cylinder.
Advantageously, the piston 100 operates such that the bowl 114
forms a reentrant bowl, which has a higher tolerance to retarded
injection timing. Reentrance describes a condition in which fuel is
injected into a generally concave feature formed at the top of the
piston, such as the piston bowl 114, which forces a moving mass of
fuel and air to circulate within the bowl and provide a more
complete and efficient combustion that produces lower emissions
than other engines. In the embodiment described herein, the bowl
features operate to split the hot injector fuel plume that is
provided to the cylinder when the piston is close to a top dead
center position in the cylinder, and also which may be provided
while the piston is approaching the top dead center position (e.g.,
pilot injection events) and/or is moving away from the top dead
center position (e.g. post injection events during a combustion
stroke). In other words, the bowl 114 is advantageously configured
to increase the beneficial range of crankshaft angles over which
fuel injected into the cylinder will benefit from reentrant
features of the piston to lower engine emissions and increase fuel
efficiency.
It is posited that the increased range over which the beneficial
fuel reentrant features can be realized results from the stepped
lip features created within the bowl, which in the illustrated
embodiment are denoted as the first lip 208 and the second lip 212,
as shown in FIG. 2. The side portions of the bowl, which can also
be referred to as the flank edge, forms a double radius by
incorporating the second surface 210 and the third surface 214,
each having a concave shape that defines, at least partially, a
toroidal cavity within the bowl. These toroidal cavities are
believed to create swirling and turbulent motion in the burning
fuel/air mixture that is pushed therein during an injection event,
which assist in mixing additional air into the burning fuel and
thus helps eliminate unburned or partially burned pockets of fuel
and combustion products by oxidizing these substances to produce a
more complete fuel burn.
As an additional advantage, by directing and/or generally confining
the fuel into a central region of the cylinder, the fuel plume, a
fuel atomization cloud, and/or a flame of burning fuel during these
times of engine operation can be redirected in terms of flow
direction and material dissipation in a fashion that reduces
exposure of the various surrounding in-cylinder combustion surfaces
to flame temperatures. By insulating cylinder surfaces from flame
temperatures, retained heat and heat transfer to the metal of the
surrounding engine components can be reduced, which in turn can
provide a higher power output and/or higher power density to the
engine, and also improve component reliability and service life. In
the illustrated embodiment, the piston 100 achieves flow detachment
along the crown surface 118 and material turbulation within the
bowl 114 by the combined effects of the features formed in and
around the bowl.
All references, including publications, patent applications, and
patents, cited herein are hereby incorporated by reference to the
same extent as if each reference were individually and specifically
indicated to be incorporated by reference and were set forth in its
entirety herein.
The use of the terms "a" and "an" and "the" and "at least one" and
similar referents in the context of describing the disclosed
embodiments (especially in the context of the following claims) are
to be construed to cover both the singular and the plural, unless
otherwise indicated herein or clearly contradicted by context. The
use of the term "at least one" followed by a list of one or more
items (for example, "at least one of A and B") is to be construed
to mean one item selected from the listed items (A or B) or any
combination of two or more of the listed items (A and B), unless
otherwise indicated herein or clearly contradicted by context. The
terms "comprising," "having," "including," and "containing" are to
be construed as open-ended terms (i.e., meaning "including, but not
limited to,") unless otherwise noted. Recitation of ranges of
values herein are merely intended to serve as a shorthand method of
referring individually to each separate value falling within the
range, unless otherwise indicated herein, and each separate value
is incorporated into the specification as if it were individually
recited herein. All methods described herein can be performed in
any suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as") provided herein, is
intended merely to better illuminate the invention and does not
pose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention.
Preferred embodiments of this disclosure are described herein.
Variations of those preferred embodiments may become apparent to
those of ordinary skill in the art upon reading the foregoing
description. Skilled artisans are expected to employ such
variations as appropriate. Accordingly, this disclosure includes
all modifications and equivalents of the subject matter recited in
the claims appended hereto as permitted by applicable law.
Moreover, any combination of the above-described elements in all
possible variations thereof is encompassed by the disclosure unless
otherwise indicated herein or otherwise clearly contradicted by
context.
* * * * *